Methods for sample analysis:

For the primary objective and outcome/ endpoint of the study, bacterial content of infant stool will be analyzed by:

• Mass spectrometry to assess intestinal content (metabolome). Techniques have been established in the laboratory of Prof. U. Sauer who already collaborated with the investigators' group in previous studies.
• 16S ribosomal ribonucleic acid (rRNA) sequencing for bacterial species composition as well as microbial diversity.
• Bacterial full genome metagenomics shotgun sequencing to identify bacterial genes present (metabolic potential of the microbiota).
• Bacterial mRNA sequencing to assess transcription and a functional role of the microbiota (metabolic activity of microbiota).
• Analysis of the intestinal virome and eukaryotic intestinal populations by appropriate sequencing or culturing techniques.
• Analysis of immunoglobulin A (IgA) antibodies in human milk and stool and the interaction of antibodies with intestinal bacteria.

For the secondary endpoints identical analyses will be performed in skin swabs, maternal milk, maternal vaginal swabs, maternal placenta probes and maternal stool. Parameters for infant growth, neurodevelopment, immune maturation and potential occurrence of pathology will be assessed at every visit. Maternal and infant nutrition, hygiene, socioeconomic status and clinical history will be assessed by questionnaires at every visit.

Further follow-up experiments with the acquired samples are possible. Specifically, individual bacteria strains can be isolated and cultured in vitro and also tested alone or in combination in experimental animals.

Bacterial sequencing by the methods described above will also inevitably identify maternal or infant DNA sequences, since metagenomic shotgun sequencing cannot differentiate between bacterial and human DNA. These human DNA sequences will not be analyzed within the scope of this project. However, these sequences might be the subject of future studies. Study participants will therefore be asked for permission to analyze human DNA from mother and/ or child at the page for "further analyses" within the consent form. An option to "opt out" for human DNA analysis will be provided and refusal will not lead to exclusion from the study.

Any findings of clear relevance to the health of the participant (i.e. mother or child) will be reported to the participant in collaboration with their treating pediatrician. Participants will need to inform the study team if they do not wish to be informed.